Fix #1632: Added alt attribute to the field image. (#2178)
Fix #1632: Added alt attribute to the field image. (#2178)

* Added alt for field image.

* Removed lint issues.

rachel-fenichel/blockly,rachel-fenichel/blockly,mark-friedman/blockly,mark-friedman/blockly,nickmain/blockly,google/blockly,twodee/blockly,twodee/blockly,rachel-fenichel/blockly,mark-friedman/blockly,twodee/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,picklesrus/blockly,google/blockly,mark-friedman/blockly,google/blockly,twodee/blockly,joshlory/blockly,google/blockly,picklesrus/blockly,nickmain/blockly,rachel-fenichel/blockly,twodee/blockly,picklesrus/blockly,nickmain/blockly,mark-friedman/blockly,twodee/blockly,mark-friedman/blockly,joshlory/blockly,rachel-fenichel/blockly,nickmain/blockly,nickmain/blockly,google/blockly,joshlory/blockly,google/blockly,google/blockly,nickmain/blockly